I know of several great VM's for System and Web application hacking, but I was curious if there were any emulators or VM's that had Network based challenges? I have GNS3, and I've used it from time to time.. but it loves to act up, and I would prefer something I could explore more

GNS3 is a front-end GUI for dynamips/dynagen, so if the problem is GNS3 itself, you may be able to get around that by working directly with the command line/text configurations. That's the closet thing I know of, unfortunately.

Your best will be snagging some used gear on eBay or somewhere else. You can get a lot of functionality for fairly low prices.